Since 1922, insulin has been the only available therapy for the treatment of type 1 diabetes and other conditions related to the lack of or diminished efficacy or production of insulin. However, diabetic patients on insulin do not have normal glucose metabolism, because insulin is only part of the missing and aberrant pancreatic function. Despite decades of research and the advent of pancreatic islet transplantation in 1974 and newer claims of success resulting from the Edmonton Protocol for islet transplantation, these approaches have not been very successful in the United States. For example, at four years post-transplant, fewer than 10% of patients who have received islet transplants remain insulin independent. Additionally, there is an 18% rate of serious side effects.
Investigators have also researched whether endogenous production of insulin can be stimulated by drug treatment. For example, over the past several decades, several therapies have been studied which are involved in glucose metabolism, and analogs of these peptides have been identified. These therapies include sequences which are similar to Glucagon Like Peptide-1 (GLP-1) and include: GLP-1 receptor analogs, Exendin-4, Exenatide/BYETTA™, which is derived from the Gila Monster, Gastric Inhibitory Peptide/Glucose-Dependent Insulinoptropic polypeptide (GIP), and compounds homologous to GLP-1, such as Liraglutide (NN2211), Dipeptidyl Peptidase-4 Inhibitors, which inhibit the breakdown of GLP-1, Gastrin, Epidermal Growth Factor and Epidermal Growth Factor Analogs, and Hamster derived Islet Neogenesis Associated Peptide (INGAP).
More specifically, hamster INGAP fragments have been identified (see Ronit, R, et al. Journal of Clinical Investigation May 1997, vol 99 (9): 2100-2109; U.S. Pat. No. 5,834,590; and U.S. Patent Application Publication No. 2004/0132644). Hamster-derived INGAP may be effective in facilitating pancreatic islet neogenesis. However, INGAP is not a human peptide, and thus may not be as efficacious and could produce an adverse immune response in some subjects.
Proof of the elasticity of the pancreas with respect to the generation of new pancreatic islets throughout one's lifetime accompanied by pancreatic islet death or apoptosis has replaced the long held concept that the number of insulin producing islet structures is fixed at birth and maintained throughout life, whereas the plasticity and ability of beta cells to proliferate within existing islets has been well established. It is currently accepted that pancreatic islet neogenesis occurs from preexisting pancreatic cells through differentiation of progenitor cells found amongst both the endocrine and exocrine fractions of the pancreas. Data demonstrates that, even decades after the onset of type 1 diabetes, insulin producing islets can be regenerated. For example, patients with type 1 diabetes who can make normal levels of C-peptide during pregnancy. Several teams have found a paradoxical rise in C-peptide levels during the first trimester of pregnancy into the normal range in as many as one-third of all pregnant type 1 patients (Lewis et al., 1976, Rigg et al., 1980, Ilic et al., 2000, Jovanovic et al., 2001). This rise in C-peptide is accompanied by a significant reduction in insulin requirements with some patients being able to completely discontinue insulin transiently during the first trimester of pregnancy. This rise in C-peptide during pregnancy that occurs within 10 weeks of gestation among patients, despite no measurable C-peptide prior to pregnancy, implies the restoration of functioning islet structures. It is hypothesized that the islet neogenesis that occurs during pregnancy results from the concomitant rise in endogenous steroid production and a down regulation of the immune system preventing immune attack on the fetus, which likely also plays a role in suppression of lymphocyte attack on the islets. Along with immune suppression, it is also speculated that there is an up regulation of maternal islet growth promoting factors during pregnancy to compensate for the lowering of the maternal glucose setpoint in pregnancy. Similarly, patients who have been on long term immunosuppression for kidney transplantation have been observed to regenerate insulin producing islets.
Over the past decade, clinical trials have been conducted to evaluate the impact of a number of immune modulators that may arrest the destruction of the beta cells of the pancreas. Anti CD-3 antibodies (hOKT3γ1 (Ala-Ala and ChAglyCD3) that target the immune response and specifically block the T-lymphocytes that cause beta cell death in type 1 diabetes have been utilized, as have, Sirolimus (Rapamycin), Tacrolimus (FK506), a heat-shock protein 60 (DIAPEP277™) an anti-Glutamic Acid Decarboxylase 65 (GAD65) vaccine, Mycophenolate Mofetil alone or in combination with Daclizumab, the anti-CD20 agent, lysofylline, Rituximab, Campath-1H (Anti-CD52 Antibody) and Vitamin D, IBC-VSO vaccine which is a synthetic, metabolically inactive form of insulin designed to prevent pancreatic beta-cell destruction, interferon-α vaccination using CD4+CD25+ antigen-specific regulatory T cells or a similar agent is used in the combination therapy approaches to utilizing regulatory T cells either directly or through the use of immunotherapy to arrest the destruction of insulin-producing cells. The aim of these trials is to determine the ability of such agents to preserve islet function by preventing further immune attack on the beta cells of the islets of the pancreas.
Additionally, recent studies have found that vitamin D may play an important immune modulating role in the prevention of type 1 diabetes. Up to 54.7% of populations in the US, regardless of latitude, have low 25 hydroxyvitamin D levels (Holick, J Clin Endorinol Metab 2005; 90-3215-3224). Vitamin D deficiency has been demonstrated, not only to be associated with the increased risk of type 1 diabetes and seen at the onset of type 1 diagnosis, but also is commonly seen among both patients with type 1 and 2 diabetes. Maintaining levels above 40 ng/ml are recommended to sustain normal immune function (Riachy Apoptosis. 2006 February; 11(2):151-9. Holick. Mayo Clin Proc. 2006 March; 81(3):353-73, Grant. Prog Biophys Mol. Biol. 2006 Feb. 28; [Epub ahead of print]. DiCesar. Diabetes Care. 2006 January; 29(1):174, Reis. Diabetes Metab. 2005; 31(4 Pt 1):318-25, Pozzilli. Horm Metab Revs. 2005; 37(11):680-3). No adverse effects have been seen with dosages up to 10,000 IU/day (Heaney. Am J Clin Nutr, 204-210, Vieth. Am J Clin Nutr. 2001; 73:288-294).
To date, however, there has been no single or combination therapy that has been successfully used to treat the underlying disease mechanisms of type 1 diabetes, type 2 diabetes or conditions in which there is a lack of or diminished insulin production and/or alterations in glucose metabolism or insulin secretion, including obesity, overweight, insulin resistant syndromes and the metabolic syndrome. There remains a need for new treatments methods and pharmaceutical compositions, which address the underlying mechanisms for the alterations in type 1 diabetes mellitus, type 2 diabetes mellitus and conditions in which there is an alteration in insulin secretion. Especially needed are methods and compositions that can also treat the many other conditions in which the lack of, or diminished, insulin production has a causative role or contributes to the symptoms of patients in need of treatment. At present, there appears to be no treatment that ameliorates the symptoms of type 1 diabetes by targeting the mechanisms underlying all of these disease states. The present invention meets the need for improved therapies for treating type 1 diabetes, type 2 diabetes and other conditions.